The present invention relates generally to electric power generation. More particularly, the present invention provides a system and method for using hybrid pulsed detonation engines (PDEs) in electric power generation.
It is well accepted that detonation is a much more efficient form of combustion than deflagration. Consequently, PDEs have a very high theoretical efficiency. Due, in part, to their high efficiencies, PDEs are receiving increased interest as a viable propulsion system for supersonic and hypersonic aircraft. The Chapman-Jouget (C-J) detonation process yields higher pressures and temperatures in cycle thermal efficiencies, which exceeds that of conventional jet engines.
In conventional gas turbine engines, a compressor is used to increase the static pressure of the fluid before heat addition within the combustor. The gas turbine engines are modeled on the Brayton engine cycle, which features a constant pressure heat addition. Gas turbines have a drawback in that while the total temperature is increased, the total pressure of the fluid suffers a very small drop and the density of the fluid drops significantly. In contrast, in PDEs, a compressor is not required because detonation waves do the work of compressing the gas and deriving energy from the fuel. The constant volume detonation combustion process causes a rapid and extreme increase in pressure, temperature and density, whereby much more useful work can be produced from the working fluid. Thus, the PDEs are extremely efficient in the use of the fuel energy.
In addition to their high efficiencies, PDEs also have simpler design geometries and fewer moving parts compared to conventional engines, thereby reducing overall costs and also making them compact, in terms of cross sectional area.
The advantages above, including efficiency and compact size, make the PDE a desirable candidate for incorporation into an electric power generation system. PDE-driven electric generators could also be desirable for co-generation and combined cycle power production, such as with the addition of fuel cells and/or steam production systems.
PDEs being small and light, can be easily maintained and hence can be used for residential or small-scale power generators, which today make use of internal combustion reciprocating engines running on gasoline. It is widely known that the more popular gasoline engines are less efficient than diesel engines. PDEs, which have higher theoretical efficiencies than the diesel engines, would be able to deliver better fuel efficiencies. A PDE-based power generator could provide a compact and portable power source for remote or emergency situations.
PDEs can be run on a wide variety of fuels, including cheap readily available fuels such as methane, propane, natural gas, coal gas, etc. The ideal PDE fuel would be hydrogen, and as such it is ready for future fuel systems. Liquid fuels, such as gasoline, kerosene, jet fuels, etc., that can be gasified, can also be used in PDEs. Detonations also produce a more thorough combustion of the fuel, thereby reducing the emissions of carbon monoxide. PDE-powered electric generation has environmental advantages over conventional generation methods, such as coal-fueled generation systems.
FIG. 1 illustrates a conventional electrical power generation system 100 employing a gas turbine engine 110. A large compressor 120 feeds compressed air into the intake of the jet combustor 110, where fuel is mixed and continuously burned to produce energy. A conventional turbine 140 is driven by the exhaust of from the combustor. The turbine 140 and gearing 150 includes a speed governor and a transmission system. The gear 150 transfers the rotational motion to the shaft of a generator 160, run at constant speed.
While PDEs do have advantages over conventional jet engines, they also pose challenges to their use in electric power generation. For example, when integrating a turbine with a PDE, the turbine blades will be subjected to shock waves, very high pressures and temperatures. The turbine blades can be protected in these harsh conditions by including a detonation diffracting plenum chamber and a shock deflecting stator stage before the multiple rotor stages of the turbine. The plenum chamber has a larger cross sectional area than the detonation chamber. The exhaust from the one or more detonation tubes flows into the plenum before being channeled into the turbine chamber, as seen in FIG. 2A 230 and FIG. 4. Studies have shown that turbines can survive repetitive detonations (shock waves) with no significant damage. (Rasheed et al., 41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Tucson, Ariz., 2005, AIAA-2005-4209).